1. Field of the Invention
The present invention relates to an imaging lens, suitable for an imaging device equipped with solid imaging elements.
2. Description of the Related Art
In recent years, the prevalence of portable electronic imaging devices, such as cellular phones, digital cameras and the like, has been spreading widely. Recent reductions in the size of electronic imaging devices has lead to demand for smaller imaging lenses equipped on electronic imaging devices. In response to such demand, numerous imaging lenses have been proposed, such as those disclosed in Japanese Patent Application Laid-Open Publication Nos. 2006-163340; 2006-284620; 2002-228922; and 2006-98976.
The imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-163340 includes three lenses arranged in three groups and employs only lenses made of a plastic material. The imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-284620 is a wide angle lens realizing fine chromatic aberration correction by cementing lenses made of a plastic material. The imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2002-228922 is a lens realizing fine chromatic aberration correction by cementing lenses made of a glass material. Further, the imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-98976 is a lens that incorporates a low dispersion glass in a first lens group to realize fine chromatic aberration correction.
Recent demand for higher image quality has accelerated advances in high pixel formation of imaging elements. In general, high pixel formation of an imaging element is achieved by minimizing the cell size thereof or by enlarging the imaging element. However, in the former case, light intensity deteriorates, and in the latter case, chromatic aberration can not be easily corrected because the focal length of the imaging lens has to be lengthened.
Although a lens formed of a low dispersion glass material, such as the lens as disclosed in Japanese Patent Application Laid-Open Publication No. 2006-98976, may overcome such problems, the production cost of the imaging lens increases since the low dispersion glass material is expensive. Also, there is a problem of increased weight resulting from the use of glass material. With respect to the imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2002-228922, although use of a low dispersion glass material in a cemented lens enables correction of chromatic aberration, problems similar to those associated with the imaging lens disclosed in Japanese Patent Application Laid-Open Publication No. 2006-98976 arise.
Meanwhile, with the imaging lenses respectively disclosed in Japanese Patent Application Laid-Open Publication Nos. 2006-163340 and 2006-284620, the range of choice concerning refractive index/dispersion ratio is narrow for resin materials, making correction of chromatic aberration caused by high pixel formation of the imaging element difficult.
In order to overcome the problems of above mentioned prior arts, an object of the present invention is to provide a small, low-cost, and light-weight imaging lens having high optical performance satisfying high pixel formation of imaging element, even when inclusive of a lens formed of resin.